1. Field of the Invention
The present invention relates to a control device for a legged mobile robot, such as a bipedal robot.
2. Description of the Related Art
As a technique for enhancing the stability of the posture of a legged mobile robot, which travels by moving a plurality of legs extended from a base body, the technique disclosed in, for example, Japanese Patent No. 3269852 has been proposed by the applicant of the present application.
According to the technique, a state amount deviation of an actual posture of the body of a robot from a desired posture is observed, and an operational moment (an operational moment about a desired ZMP) to be additionally applied to the robot is calculated according to a PD law (proportional-differential law) from the observed value of the state amount deviation as the feedback manipulated variable (control input) required to converge the state amount deviation to zero.
Further, the operational moment is divided into an actual robot manipulation moment to be directly applied to an actual robot and a model manipulation moment to be applied to a robot in a dynamic model for generating a desired gait of the robot.
In the actual robot, the motions of the actual robot are controlled by compliance control such that the actual motion of the robot follows the motion of a desired gait (desired motion). Further, in the dynamic model, a desired gait of the robot is generated such that a model manipulation moment is generated about the desired ZMP.
Thus, in the case where the actual posture of the body of the robot deviates from a desired posture due to a disturbance or the like, a floor reaction force moment for eliminating the deviation is applied to the robot.
Further, a technique for generating in real time a desired gait that permits a continuous motion of a robot has been proposed in, for example, Japanese Patent No. 4246638 by the applicant of the present application. According to the technique, a desired gait is generated such that the motion of the desired gait to be generated anew is converged to a virtual reference motion, which is a future convergence target.
In the technique, to generate the time series of a new desired gait, a cyclic motion in which a motion of the same pattern is repeated is set as a reference motion (the motion of a normal gait). Then, the time series of the new desired gait is generated such that the time series of the new desired gait is converged to the aforesaid reference motion in the future. The technique disclosed in Japanese Patent No. 4246638 adopts the technique disclosed in Japanese Patent No. 3269852. In this case, according to the technique disclosed in Japanese Patent No. 4246638, the motion of a desired gait is sequentially determined by determining the trajectory of a desired ZMP such that the motion of a desired gait to be generated anew can be converged to a reference motion and the aforesaid model manipulation moment is generated about the determined desired ZMP.
In the technique disclosed in Japanese Patent No. 4246638, the reference motion providing the future convergence target of the desired gait to be generated anew is set on the assumption that the moment in the motion (specifically, the horizontal component of the moment) about a desired ZMP is zero. Therefore, the trajectory of the desired ZMP in the motion of the desired gait to be generated anew is also determined on the assumption that the horizontal component of the moment about the desired ZMP in the future will be zero.
Meanwhile, when the instantaneous value of the motion of a desired gait is sequentially determined using the trajectory of the desired ZMP determined as described above, the instantaneous value of the motion is determined such that the aforesaid model manipulation moment is generated about the desired ZMP on a dynamic model. In this case, the aforesaid state amount error related to the posture of a robot 1 does not usually converge to zero instantly. Hence, there are cases where a state in which the aforesaid non-zero model manipulation moment is fed back to the dynamic model for generating gaits lasts for a relatively long period of time.
In such a case, there is a possibility that the motion of the desired gait to be actually generated deviates from an appropriate motion that converges to the reference motion, which is the convergence target. As a result, a motion of a desired gait that makes it difficult for the robot 1 to accomplish a continuous motion may be undesirably generated.